Self-stabilizing submarine tank

ABSTRACT

A submarine tank formed of pre-stressed concrete comprises central cells and outward peripheral ballast cells. The cells are interconnected and can be filled with liquid hydrocarbons. Appropriate control means can be provided for effectuating the controlled submerging of the tank. Vertical pillars can be provided to remove any vertical force effect of swells. Lower stud members can be provided on the bottom of the tank.

United States Patent .[191

Lacroix [451 Feb. 26, 1974 SELF-STABILIZING SUBMARINE TANK [7 5]Inventor:

[73] Assignee: Sea Tank Co., Paris, France [22] Filed: Mar. 6, 1972 [21]Appl. No.: 231,933

Roger Lacroix, Sceaux, France [30] Foreign Application Priority DataMar. 5, 1971 France 71.07723 [52] US. Cl. 6l/46.5, 61/50 [51] Int. Cl.865g 5/00, E02d 27/38 [58] Field of Search..... 6l/46.5, 46, .5, 50;114/57;

[56] References Cited UNITED STATES PATENTS Roulet et a1. 61/46 Starr etal. 6l/46.5

2,938,353 5/1960 Vorenkamp.... 61146.5 3,396,544 8/1968 Manning 61/46.5X 3,385,464 5/1968 Courbon 6l/46.5 X

Primary Examiner-Jacob Shapiro Attorney, Agent, or FirmSughrue,Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A submarine tank formed ofpre-stressed concrete comprises central cells and outward peripheralballast cells. The cells are interconnected and can be filled withliquid hydrocarbons. Appropriate control means can be provided foreffectuating the controlled submerging of the tank. Vertical pillars canbe provided to remove any vertical force effect of swells. Lower studmembers can be provided on the bottom of the tank.

5 Claims, 4 Drawing Figures PATENTEDFEBZB 1914 3,793,842 SHEET- 2 BF 2FIG .3 ?=f 23 1 SELF -STABILIZING SUBMARINE TANK BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates tosubmarine tanks, more particularly for hydrocarbons, made of prestressedreinforced concrete, comprising several cells located between twoplates. The lower plate or apron is substantially planar, and rests onthe sea bed, the upper plate has an upswept shape and acts as a coveradapted to receive connections to the cells and the operating unitnecessary for using the tank for storing fluids.

2. Description of the Prior Art The submarine tanks produced up to nowhave had various disadvantages that result from the complexity of theirconstruction. Further, there is a danger of instability when they aresubmerged and, once laid on the sea bed, and also subject to the effectsof the swell and of sea currents.

SUMMARY OF THE INVENTION The object of the present invention is toremedy the various past defects by producing a structure having inherentresistance, comprising, on its periphery, compartments speciallyintended for ballasting the structure and by the specialization of thevarious compartments for functions facilitating the submergingoperation, the structure having on its lower plate, ribs jutting out toresist horizontal movement after it has been laid in position.

A characteristic of the present tank is that its constituent cells areformed into two types of compartments, the ones forming a reinforcedcore having an upswept cover, the others, called ballastingcompartments, being peripheral and downswept.

BRIEF DESCRIPTION OF THE DRAWINGS in FIG. 2;

FIG. 2 shows a vertical cut-away view of the tank along ll--II in FIG.1; FIG. 3 shows a tank in an elevation view, provided 7 with an emergingcolumn;

FIG. 4 shows a tank in an isometric projection in the mode ofconstruction by elements assembled at sea, on the surface.

SUMMARY OF THE INVENTION FIGS. 1 and 2 show, at l, the peripheral partof the tank that is used for the ballasting cells. The part 2 is theresisting core shown here as a truncated pyramid with square bases. 3vis a ballasting cell and 4 is a cell of the resisting core. Theresisting core is separated sure can be either the pressure of the totalheight of the sea water, for current depths in the order of a hundred orso metres, or that which separates two consecutive submerging levels forgreater depths.

Openings are made in the walls separating the cells to allow them tocommunicate with one another. To provide a more versatile aspect for therelative use of the tank as well as mastering of problems concerned withits submerging, it should be possible to cut off communications betweencertain cells, and to do this, the corresponding openings are providedwith waterproof doors which, when operated, enable respectively thecutting off and the establishing of the communication between adjacentcells. On the walls of the cells of the core there are openings 7a atthe lower part, and 7b at the upper part, whereas on those of theballasting cells 3, openings 70 are provided. The gates with whichcertain of the openings are fitted have not been illustrated.

Inasmuch as concerns the ballasting cells 3, they are grouped togetherinto compartments of two types: angle compartment 13 with five cells andintermediate compartments 14 with six cells having substantially thesame capacity. The cells of a same compartment communicate with oneanother, by openings 70 in their walls.

from the ballasting compartments by the wall 5. This wall 5 and theplates, respectively 9 forming the cover, and 10 forming the apron, aresupported, moreover, by vertical walls 6 separating the cells andembedded in the plates to resist against great differences in pressurebetween the outside and inside. This difference in pres- The fourcompartments of a same type form a group of cells which can be filledsimultaneously and independently from those of the other group.

The empty tank floats and, at 15, FIG. 2, its empty water line isillustrated.

To fill the ballasting cells with water, all that is necessary is toopen the valves of a manifold, not illustrated, taking water frombeneath the line 15 and bringing it to the lower part of one of thecells of a compartment, whereas the air escapes through a circuitconnected to the upper part of the cell and ending up at the operatingunit, in which the corresponding control valves are arranged.

When the cells of the four compartments of a group are completely filledwith water, the water line moves up to 16, whereas after completefilling of the cells of the second group, the water line then moves upto 17, at a distance in the order of a metre from the upper base of thetruncated pyramid having square bases forming the cover 9 of the corehaving inherent resistance. The head-room thus provided for the tankensures the required stability of the latter during towing.

It need hardly be mentioned that the subdivision of the ballasting cellsinto a greater number of compartments and into various groupings of thecompartments should be considered if the need is felt, while respectingthe balancing rule specifying that compartments having the same capacityplaced symmetrically in relation to the axis of symmetry of the tankshould be filled simultaneously.

Inasmuch as concerns the cells of the core, they are also groupedtogether into compartments having specific functions during thesubmerging of the tank. These cells are grouped into compartments ofthree types: a central compartment 18 acting as an extra'ballasting andtaking part, due to its progressive and partial filling, in thesubmerging operation, four balancing compartments 19 used for removingthe faulty balance by selective filling of the latter and, lastly, fourstorage compartments 20 remaining empty during submerging.

A pumping system, not illustrated, enables water to be brought into thebase of the compartment 18, whereas air is evacuated from the upperpart. This system can be reversed and enables, in case of need, theunballasting of the compartment.

Balancing by the compartments 19 can be effected with a constant volumeof water without modifying the water line, by pumping water from thecompartment 19 in which suitable pumps and hydraulic circuits areprovided for that purpose; on the other hand, the grouping together'ofthese cells into compartments momentarily independent from one anothercancels the water ballast effects.

The dimensions of the tank, the total number of the cells and the numberof cells assigned to the functional compartments organized for thesubmerging operation are connected with the dimensions of the tank, theproduct to be stored and the storage conditions of the product.

The plate forming the apron can be thickened at 11 in order to embodythe support surface of the tank on the bottom. The spade studs, whichcan possibly be arranged on the outside of the apron, are shown at 12.These studs are intended to improve, according to the kind of sea bed,the resistance of the tank to horizontal movement, and also to avoid anypossible erosion caused by undercurrents. The tank rests on the sea bedby its own weight which is sufficient to counteract the alternatingvertical efforts of the swell which would tend to lift it periodically;nevertheless, the hollow pillars 21, FIG. 1, are arranged vertically inthe compart ments which they pass through from one end to the other, tobalance permanently the pressures exerted on the lower and upper plates,of the tank, and hence to compensate the effects of the verticalcomponents of the swell on the tank.

When the tank is submerged to a shallow depth, it is then arranged so asto resist the total pressure exerted at the end of the submerging, whichcan then be effected in a continuous way by continuous injection ofwater in the extra ballasting compartment 18.

For a greater depth, submerging requires, in that case, stoppages atimtermediate levels, spaced out vertically at heights definedpreviously, and corresponding to the permissible differential pressure.At these levels, all the compartments of the reinforcing core and filledwith a compressed gaseous fluid enabling the outside water pressure tobecome balanced again and submerging to be resumed down to the nextlevel. In that case, the inherent resistance of the tank is then onlypartial; but in relation to known structures which are less resistant,it enables the number of levels required during submerging to bereduced. The actual submerging operation can be controlled; either byfloats arranged in chains round the tank, the floats of each chain beinglinked together by an anchor chain; or by a pillar rising above the tankand constantly remaining above the surface. This pillar can subsequentlyconnect the tank for the material to be stored therein with possibleaccess to the control valves at the upper part of the tank which can beassigned for that purpose, and the positioning of the superstructureswhich can be installed at its summit easier.

FIG. 3 shows an elevation view of the tank provided with such anemerging pillar 22; it enables submerging to be controlled, access tothe control valves placed above the tank and, possibly, as is known, anupper platform 23 to be arranged above the level 24 of the sea.

After the submerging of the tank, and the laying of the latter on thesea bed according to techniques suited to the kind of sea bed, allcommunications are again established between the cells of the variouscompartments, both by opening gates and by manipulating the valves ofthe various circuits connected to the control unit. The tank is thencompletely filled with sea water, when the air has been completelyremoved, whereas the ballasting compartments filled with water at thebeginning of the submerging operation are cut off from the sea water,the corresponding valves being closed. Then the connection is made, atthe level of the control unit, with the fill pipes for the fluid to bestored, in this case, hydrocarbons. After having re-established thecommunication of the ballasting compartments with the sea, thehydrocarbons, which remove the sea water, can then be injected into thetank. Injection is thus effected under pressure. Injection is stoppedwhen a volume of hydrocarbons sufficient for filling the tank up to aheight less than one metre, for example, from the total height has beeninjected, thus leaving a water clearance.

The pumping of hydrocarbons can be effected either by allowing the oilto flow subsequent to the pressure exerted by the sea water, or bysetting up a pressure by pumping.

As is known, the various openings 7a, 7b and providing communicationbetween the cells, take part in the stabilization of the water tohydrocarbon interface, in combination with the dimensions of theorifices for making the tank communicate with the sea. Thisstabilization is valid both for movements caused during filling oremptying and for movements caused during filling or emptying and formovements due to the swell and to sea currents. It can then be notedthat there is an attenuation and a dephasing of the interface movementsin relation to the movements caused by the sea, more particularly by theswell.

The apparent weight of the tank completely filled with hydrocarbons issufficient, despite the lightening force created by the difference indensity between hydrocarbons and sea water, to provide a pressure on thesea bed opposed to lifting and sliding of the tank.

Thus, a total stability of the reservoir, both during towing andsubmerging is obtained by the value of its metacentric head, which iskept high, and during use, by the combined action, of its weight and ofthe compensation of the efforts exerted by the swell.

Inasmuch as concerns construction, the tank illustrated in FIGS. 1 and 2is built entirely on land, in an excavation, then floated to itssubmerging site.

According to another method of construction, the tank is made of severalelements, prefabricated on land, floated to a calm water site where theyare assembled so as to form a single tank which is then towed to itssubmerging site.

FIG. 4 shows a tank according to this method of construction, comprisingprefabricated elements 25 and assembled at sea: by way of an example,three elements 25 have been illustrated. The lines 26 show thefluidtight assembling lines. Here, also, the ballasting compartments,placed in the downswept part 27 of the tank and the higher reinforcedcore in the part 28 can be distinguished. This leads to the forming of aparallelepiped having horizontal generating lines, from modular elementsenabling the constructing of tanks having different capacities, usingidentical and recurring elements, whose number depends on the capacityrequired. These tanks thus formed and having the advantages of low cost,and the versatile qualities of modular construction, can have anemerging pillar such as 22 in H6. 3 rising above them, and the cellswhich they contain can be grouped in compartments assigned tospecialized functions to take part in the submerging of the tank andthen assigned to general functions during use.

The various walls and partitions are pre-stressed in two directions, andconsidering the effort exerted at the level of the embedded joints, thetank is then under three-dimensional pre-stress. Both the inner andouter surfaces of the tank can be coated with known materials, moreparticularly, synthetic resin, to prevent their corrosion and to improvetheir fluid-tight qualities, and can be physiochemically treated in aknown way to counteract the effects of sea water and of the fluids to bestored therein.

It should be noted that the invention is in no way limited to theparticular form of embodiment which has just been described, but that itcomprises all possible variations corresponding to the generaldefinition thereof which has been given.

Thus, while a tank having a square shape is shown in the drawing, othershapes such as a rectangular shape may meet the requirements of thepresent invention.

Likewise, the example given of the hydrocarbon storage tank is only onepossible application. More particularly, submerged tanks comprise anyhollow body which can be submerged by specialization of the compartmentsit comprises, so as to effect, so to speak, automatic submerging; and,in this case, a container which submerges itself by the means described,will be considered as a submerged tank.

What is claimed is:

1. In a pre-stressed concrete submarine storage tank formed by aplurality of scaled cells extending between an upper cover plate and aflat lower plate resting on the sea bed, the improvement wherein: saidplates are similarly rectangular, of generally equal size, with saidupper plate being of truncated pyramidal shape at its center, said cellsare grouped into multiple types of sealed core and peripheralcompartments including means for effecting fluid communication betweencells of the same compartment, and wherein; said cells extending aboutthe periphery of said tank are shorter in height than the sealed corecells and comprise two types of peripheral compartments with allperipheral compartments of the same type being symmetrical in relationto the axis of symmetry of said tank, and means are provided for fillingall peripheral compartments of the same type simultaneously with seawater to act as ballasting compartments or with fluid hydrocarbon to actas storage compartments, said core cells internal of the peripheralcompartments are taller and include at least one central compartmenthaving means for progressively and partially filling said centralcompartment cells to control submerging of said tank, and said corecells further form at their four corners thereof, complementary ballastcompartments and means are provided to control filling of saidcomplementary ballast compartments for facilitating submerging of saidtank, and a plurality of storage compartments surround said centralstorage compartment, between said central compartment and saidperipheral compartments, and have means for selectively filling saidstorage compartments with fluid hydrocarbon subsequent to submerging ofsaid tank.

2. A submarine tank as in claim 1 wherein the peripheral ballastingcells are of such a size relative to the central cells that when onlythose cells are filled withwater the tank will float.

3. A submarine tank as in claim 1 further including lower stud membersattached to the lower plate which help prevent relative errosion of thesea bed beneath the tank.

4. A submarine tank as in claim 1 further including hollow verticalpillars passing from the bottom to the top of the tank and open to thesea water, whereby the vertical lifting effects of swells of water areneutralized.

5. The submarine storage tank as claimed in claim 1, further comprisingmeans for filling said core compartment cells with compressed gaseousfluid to balance the water pressure acting on the tank duringsubmergence.

1. In a pre-stressed concrete submarine storage tank formed by aplurality of sealed cells extending between an upper cover plate and aflat lower plate resting on the sea bed, the improvement wherein: saidplates are similarly rectangular, of generally equal size, with saidupper plate being of truncated pyramidal shape at its center, said cellsare grouped into multiple types of sealed core and peripheralcompartments including means for effecting fluid communication betweencells of the same compartment, and wherein; said cells extending aboutthe periphery of said tank are shorter in height than the sealed corecells and comprise two types of peripheral compartments with allperipheral compartments of the same type being symmetrical in relationto the axis of symmetry of said tank, and means are provided for fillingall peripheral compartments of the same type simultaneously with seawater to act as ballasting compartments or with fluid hydrocarbon to actas storage compartments, said core cells internal of the peripheralcompartments are taller and include at least one central compartmenthaving means for progressively and partially filling said centralcompartment cells to control submerging of said tank, and said corecells further form at their four corners thereof, complementary ballastcompartments and means are provided to control filling of saidcomplementary ballast compartments for facilitating submerging of saidtank, and a plurality of storage compartments surround said centralstorage compartment, between said central compartment and saidperipheral compartments, and have means for selectively filling saidstorage compartments with fluid hydrocarbon subsequent to submerging ofsaid tank.
 2. A submarine tank as in claim 1 wherein the peripheralballasting cells are of such a size relative to the central cells thatwhen only those cells are filled with water the tank will float.
 3. Asubmarine tank as in claim 1 further including lower stud membersattached to the lower plate which help prevent relative errosion of thesea bed beneath the tank.
 4. A submarine tank as in claim 1 furtherincluding hollow vertical pillars passing from the bottom to the top ofthe tank and open to the sea water, whereby the vertical lifting effectsof swells of water are neutralized.
 5. The submarine storage tank asclaimed in claim 1, further comprising means for filling said corecompartment cells with compressed gaseous fluid to balance the waterpressure acting on the tank during submergence.